Hi Bernd, yes I realized that right now!
No turning off via LB…
The “problem” is: As we have seen the other day I have to put a card stock layer under the veneer because the honeycomb “burns” the wood. But I need both sides to be clean…
The card stock (very white) does not absorb the laser, so does not get cut and won’t release the air into the belly of the beast. The air bounces back under the veneer and displaces the pieces - not good!
I’ll try the valve! 
Thanks, Mirjam